U.S. Pat. No. 8,998,545 illustrates an inventive retention knob for a tool holder which substantially eliminates distortions in a tool holder tapered surface during installation of the retention knob. The '545 patent is hereby incorporated by reference.
U.S. Pat. No. 9,205,524 discloses a test gauge for checking the tapered surface of a tool holder to determine whether distortions in the surface have been created by a retention knob that is installed in the tool holder. The '524 patent is hereby incorporated by reference.